Uber-Cheap Electroscope for Teaching




Introduction: Uber-Cheap Electroscope for Teaching

About: Paul (Udon) is a Chinese-speaking South African, who likes saffron tea, sunshine, dogs, and Asian food. He can make things out of yeast, thermoplastic, Arduinos, Xamarin, C#, wood, junk plastic, metal, motors,…

The easiest and most fascinating science instrument you can make from rubbish lying around is an electroscope.

Basically, an electroscope is a device that visibly reacts in the presence of static charge by means of aluminium leaves that will spring apart.

The working principle is based on the fact that like electrical charges repel, while opposite charges attract. We can use this principle to push electrons around the scope, and by grounding the scope while in the presence of a charged object, we push electrons out or pull them in. We remove the grounding path, then remove the object that is creating the electric field. What remains is an electroscope that is either positively or negatively charged.

Huh? Don't worry, its way more simple that it sounds.

But the possibilities for using this for teaching physics are vast:

Charges, forces, current, capacitance...even ionizing radiation.

Ionizing Radiation?

Don't forget - electroscopes were used as radiation detectors in the early days of particle physics.You can build it and use gas lamp mantle as a radiation source to show that it works. Gas mantles contain thorium, the element that makes them magically produce more light when heated. If you build the electroscope and charge it with static, theoretically an old TV (electron source), or a thorium gas mantle will cause it to slowly discharge, visibly.

Note: This Instructable is an entry for the the 2017 Teachers Contest, and the Plastics Contest. If you dig this idea, and think it is a great tool for teaching students about electricity, please vote for me! I am hoping to use the prize for a basic electronics class I currently teach in South Korea. I am slowly developing low-budget but effective ways to help students fully grasp electrical concepts.

So, again: Please Vote For My Instructable!

Whatever the case, I have designed this instructable to be a useful teaching tool - feel free to use this material in your teaching!

Step 1: Parts and Tools

The following will be needed:

  1. Aluminium kitchen foil.
  2. A plastic jar.
  3. Some copper wire - thicker wire will make for a sturdier antennae, and can be found inside "single core" electrical wire, from any hardware store, or better, the junk heap.

The following tools will be necessary:

  1. A hole-punch - I got mine for $2 from Daiso in Korea! How do they make such cool crap for so cheap?! Shweet...
  2. Scissors.
  3. Pliers - for cutting the wire and shaping the corners.
  4. A glue gun - not necessary, but ideal for sealing the holes up.
  5. A drill - in my case, um, seeing at I planned on entering the Hand-Tools contest, so I literally used a drill that I turned by hand. I know. Zoom into the photo for a stupid joke...

Step 2: Assembling the Antennae

  1. Drill two holes in the lid of the jar using your stupid South African drill. Or better, use the type of drill that runs on some kind of electricity...
  2. Thread the first side of the wire through with a long enough length to create the hook that will sit inside the jar.
  3. Take the other end, and bend it carefully into a loop or two (or three...).
  4. Stick the remaining end into the second whole.
  5. Bending both ends strategically will give them more stability.
  6. Make the hook on the length that sticks into the jar.
  7. Finally, use hot-snot to to seal the two holes, as well as give the wires some final securing.

The antennae is a great opportunity for creating something funky and Doctor-Suessy. The copper wire can be found in power cables that can be bought at a hardware store. Ask for "single-core", not "stranded" wire.

I have not experimented with differing lengths of copper wire for the antennae, but longer wire theoretically is not a great thing, as it creates more surface area allows ions in the air to slowly make the device return to an uncharged state. On the other hand, it should make the device more sensitive?

Regardless, it does look pretty cool...

Step 3: The Aluminium Leaves

I found that the plastic insert that was in the lid of the jar popped out, and I realized I could use it to trace the cutout for the leaves.

  1. Cut out a teardrop shape in the plastic, preferably not too long, ideally so if fully extended in any direction, the leaves don't reach the walls of the jar. Make the top pointed to a half-hexagon-shaped end.
  2. Use this plastic stencil to trace an outline on the flattened aluminum foil. The slightest pressure from a pen is enough to create a good outline - anything harder can cause it to tear apart.
  3. Cut the outlines out, and use the punch to knock out a hole at the top of the tear-drop foil leaves.
  4. Hang them on the hook.

That easy! Close the thing up, and its ready to charge up.

Step 4: Charging Up

The easiest way to charge up an electroscope is by means of a balloon, but you can find all sorts of materials that can be charged up. Its just that it may require rubbing lots of weird objects in your hair....

  • Syrup? Nope.
  • Plastic cover? Yup.
  • Humans? Don't think so.
  • Fire? Nuh-uh.
  • Cat? Nope.

After much experimentation though, I came to the conclusion that balloons, PVC book covers, plastic packaging, and Styrofoam are some of the best ways to generate static, with balloons being the most versatile.

All involve hair rubbing.

One you have a charged object (assuming a balloon), we charge the scope up as follows:

  1. Move the charged object close to the scope. The leaves will fling apart. The length of the movement shows how much the object is charged.
  2. While keeping the object close, touch the copper antennae with your finger. The leaves will fall down. Remove your finger.
  3. Remove the charged object. The leaves swing up again! And stay like that!

That easy. This method is called induction charging, and it appears a bit mysterious. The diagrams above explain the actual process and what is going on. If the object was negatively charged, the scope will now be positively charged, and visa-versa.

What can this be used for?

Please feel free to use this with diagrams in teaching static electricity (but please give credit). If you think this is a cool way to teach students about electricity, please vote for me for the contest!

Comments, criticisms, and inaccuracies? Say something below!

Teachers Contest 2017

Runner Up in the
Teachers Contest 2017

Plastics Contest

Participated in the
Plastics Contest

Make It Move Contest 2017

Participated in the
Make It Move Contest 2017

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    7 Discussions


    2 years ago

    I was wondering if large mason jars ( glass jars with metal screw on caps) would work. Would the metal caps be a problem? If I put a styrofoam circle in the cap would that prevent leakage of charge? Would glue from the glue gun be enough protection?


    Reply 2 years ago

    Good question. It really depends on what you are using it for.

    If you are using it to teach students, and you are manually charging it up with balloons and whatnot, then safety won't be an issue, discharge won't be a big issue, and so having the extra conductive surface area on the metal jars will be no issue.
    In my mind, my silly copper aerial is functional but also makes it look interesting. Mason jars are kind of expensive though, but otherwise, I see no reason why they won't work well. The only thing to consider is that you now have more surface area, as well as an area for fingers to touch up against. Again, this might not be a bad thing.

    On the other hand, if you are using it to detect ionizing radiation, then the larger surface might not be great, because it will make the device more susceptible to moisture in the air, discharging faster.

    And the third possibility is that you are charging it up to much higher voltages, with a VanDeGraaf generator or similar. Then the possibility of exposed metal getting touched up against, or giving the high voltages something to easily arc off is not good.

    I think that the the most difficult part of the build is getting proper holes in the aluminum foil. I highly recommend getting a cheap paper punch, or using something similar to get a nice perfect hole in the alum. leaves. This is the only part that moves, and if it swings freely, the results are much better.


    2 years ago

    I also have an Instructable in the Teachers Contest, but I love your idea and your writing so I voted for you :-)


    Reply 2 years ago

    Am I doing that badly in the contest? heeheehee

    That's very encouraging - baie dankie meneer!


    Reply 2 years ago

    I meant the opposite of course, but game is on ;-) Mag die beste wen!


    2 years ago

    Hey Paul - This is a great instructable. I especially like the diagrams and clear explanation of how everything works. Excelllent work and great that you are willing to share all this knowledge with others.


    Reply 2 years ago

    Bwahaha. Thank you mister.